Slay Arix'Amal to get the Burning Legion Gate Key. Use the Burning Legion Gate Key on the Rune of Spite, then return to Nazgrel in Thrallmar.
You are an honor to us, <name>. But now we must strike before the Legion recovers! To the north of Thrallmar lies Invasion Point: Annihilator. It houses a warp-portal through which the Legion draws its reinforcements.
You must overload that portal - and blast it back to the abyss it came from. The portal's activation key will be held by the Point's commander - Warbringer Arix'Amal. Slay him. Take the key. Use it on the portal and do what must be done. May the warchief's blessings be with you.
Also, you get: 2
Hurry, <name>. Every second that warp-portal stands open, another foul demon is brought into this world!
Praise the ancients, you've done it, <name>! The Legion has suffered a terrible defeat - and Thrallmar is safe once again. Ah, if I had but a hundred warriors with your heart and cunning, this broken land would be tamed already! I salute you.
<Nazgrel salutes you crisply>
Upon completion of this quest you will gain: